Plasma vapor deposited (pvd) coating process

ABSTRACT

A plasma vapor deposited (PVD) coating method. The method includes overlaying a primer polymer layer onto a substrate surface. The method further includes overlaying a chrome metallic layer onto the primer polymer. The method also includes depositing a plasma vapor deposited (PVD) oxide layer of a thickness of 1 to 5 nanometers onto the chrome metallic layer and having a parameter of color change of the underlying chrome metallic layer. The color change may be determined according to the following equation: 
       Δ E*   ab =√{square root over ((Δ L *) 2 +(Δ a *) 2 +(Δ b *) 2 )}
 
     L is the color brightness of the oxide layer, and a and b are the color-component dimensions of the oxide and metallic layers. ΔE* ab  may be less than 2.3. The method further includes overlaying an exposed polymeric layer onto the PVD oxide layer to form a protective layer at the interface between the exposed polymeric layer and the oxide layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 14/029,341filed Sep. 17, 2013, now issued as U.S. Pat. No. ______ on ______, whichis a continuation of U.S. application Ser. No. 13/178,859 filed Jul. 8,2011, now abandoned, which claims the benefit of U.S. provisionalapplication Ser. No. 61/365,477 filed Jul. 19, 2010, all documents inwhich are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a plasma vapor deposited (PVD) coatingprocess.

BACKGROUND

Articles such as coated wheels in the art may experience coating layerfailure when exposed to contact with physical objects such as gravel orstones, as well as extreme temperatures and/or rapid temperaturechanges. It is desirable to provide wheels that are relatively resistantto one or more such layer failures.

SUMMARY

According to a first embodiment, a plasma vapor deposited (PVD) coatingmethod is disclosed. The method includes overlaying a primer polymerlayer onto a substrate surface. The method further includes overlaying achrome metallic layer onto the primer polymer. The method also includesdepositing a plasma vapor deposited (PVD) oxide layer of a thickness of1 to 5 nanometers onto the chrome metallic layer and having a parameterof color change of the underlying chrome metallic layer. The colorchange may be determined according to the following equation:

ΔE* _(ab)=√{square root over ((ΔL*)²+(Δa*)²+(Δb*)²)}

L is the color brightness of the oxide layer, and a and b are thecolor-component dimensions of the oxide and metallic layers. ΔE*_(ab)may be less than 2.3. The method further includes overlaying an exposedpolymeric layer onto the PVD oxide layer to form a protective layer atthe interface between the exposed polymeric layer and the oxide layer.

In another embodiment, a plasma vapor deposited (PVD) coating method isdisclosed. The method includes overlaying a primer polymer layer onto asubstrate surface. The method further includes overlaying a chromemetallic layer onto the primer polymer. The method also includesdepositing a plasma vapor deposited (PVD) oxide layer of a thickness of1 to 5 nanometers onto the chrome metallic layer and having a parameterof color change of the underlying chrome metallic layer. The colorchange may be determined according to the following equation:

ΔE* _(ab)=√{square root over ((ΔL*)²+(Δa*)²+(Δb*)²)}

L is the color brightness of the oxide layer, and a and b are thecolor-component dimensions of the oxide and metallic layers. ΔE*_(ab)may be less than 2.3. The method further includes overlaying an exposedpolymeric layer onto the PVD oxide layer to form a protective layer atthe interface between the exposed polymeric layer and the oxide layer.

Yet another embodiment discloses a plasma vapor deposited (PVD) coatingmethod including the step of depositing a plasma vapor deposited (PVD)oxide layer of a thickness of 1 to 5 nanometers onto the chrome metalliclayer and having a parameter of color change of the underlying chromemetallic layer. The color change may be determined according to thefollowing equation:

ΔE* _(ab)=√{square root over ((ΔL*)²+(Δa*)²+(Δb*)²)}

L is the color brightness of the oxide layer, and a and b are thecolor-component dimensions of the oxide and metallic layers. ΔE*_(ab)may be less than 2.3. The method further includes overlaying an exposedpolymeric layer to form a protective layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B respectively depict a front view and a side view of avehicle wheel according to one embodiment;

FIG. 2 depicts a cross-sectional view of surface layers of an articlesuch as a vehicle wheel according to another embodiment; and

FIG. 3 depicts a process flow of making an article such as a coatedwheel according to yet another embodiment.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein. However, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. Therefore, specific structural and functionaldetails disclosed herein are not to be interpreted as limiting, butmerely as a representative basis for the claims and/or a representativebasis for teaching one skilled in the art to variously employ thepresent invention.

Moreover, except where otherwise expressly indicated, all numericalquantities in the description and in the claims are to be understood asmodified by the word “about” in describing the broader scope of thisinvention. Unless expressly stated to the contrary, the description of agroup or class of material is suitable or preferred for a given purposein connection with the invention implies that mixtures of any two ormore members of the group or class may be equally suitable or preferred.

In durability testing of aluminum wheels having a chrome/aluminum alloy,inter-layer adhesion failure has been reported to occur between thealloy layer and an adjacent polymer or resin layer. This may resemblewhat may occur during a car wash on a cold day, or alternatively, when avehicle wheel is contacted with gravel or stones during driving. Thepresent invention, in one or more embodiments, is believed to solve theadhesion failure problems mentioned above.

In one embodiment, and as depicted in FIGS. 1A and 1B, an article suchas a vehicle wheel generally shown at 10 includes a front portion 12 andrim portion 14. To the outer surfaces of the front portion 12 and/or rimportion 14 is applied a coating system which is detailed herein, withrelatively improved inter-layer adhesion and hence greater resistance todamage from contact or temperature challenges. In the case of thearticle being a vehicle wheel, the vehicle wheel may be formed of anysuitable material such as steel, aluminum alloy, cast aluminum,magnesium, and/or magnesium alloy.

In another embodiment, and as depicted in FIG. 2, an article such as avehicle wheel generally shown at 200 includes a substrate 202 having asurface 212, to which is applied a metallic layer 206 including a firstmetal (not shown), and an oxide layer 208 contacting the metallic layer206 and including an oxide of a second metal (not shown) different fromthe first metal. In certain instances, the article 200 may furtherinclude one or more primer polymer layers generally shown at 204, whichare positioned between the metallic layer 206 and the substrate 202, thesurface 212 of the substrate 202 in particular. In the event that two ormore primer polymer layers 204 are employed, the primer polymer layers204 may be chemically different from each other. In certain otherinstances, the article 200 may further include one or more outer polymerlayers generally shown at 210. In the event that two or more top polymerlayers 210 are employed, the outer polymer layers 210 may be chemicallydifferent from each other.

Without wanting to be limited to any particular theory, it is believedthat the oxide layer 208 helps provide additional polar groups on themetallic layer 206 and/or the outer polymer layer 210 for improvedadhesion there between.

In one or more embodiments, “layer,” as referenced in the metallic layer206, the oxide layer 208, the outer polymer layer 210 and the primerpolymer layer 204, may include sub-layers of identical chemicalcomposition, each of which may be individually applied.

The primer polymer layer 204, the metallic layer 206, the oxide layer208 and/or the outer polymer layer 210 may be applied by any suitablecoating processes. A non-limiting example of the coating process is coldgas spraying, as disclosed in U.S. Pat. No. 5,302,414, which isincorporated by reference herein in its entirety. In the process of coldgas spraying, a layer is applied by spraying a high velocity flow ofpowder, which is in solid state, at a temperature which is lower thanthe melting point of the powder material. Another non-limiting exampleof the coating process is, as disclosed in U.S. Pat. No. 5,795,626,which is incorporated by reference herein in its entirety, triboelectricdischarge kinetic spraying and thermal spray technologies including highvelocity combustion, low velocity combustion, plasma spray and twin wirearc spray. Another non-limiting example of the coating process iselectrolytic coating involving one or more cationic polymers. Thepolymer coating bath may be an aqueous electrolytic bath, containingcationic polymers which may be deposited onto the surface from anelectrolytic bath.

In certain instances, the metallic layer 206 and/or the oxide layer maybe applied via physical vapor deposition (PVD). A non-limiting exampleof the PVD method is disclosed in “Coatings Durability and MechanicalReliability of PVD—Bright Chrome Coated Aluminum Wheels” authorized byCharles J. Russo, SAE 2007-01-1530, which is incorporated by referenceherein in its entirety. Without wanting to be limited by any particulartheory, it is believed that the PVD method is relatively moreenvironmental friendly than other locating methods, such as electrolyticcladding methods which often use toxic electrolytic solutions.

The primer polymer layer 204 and/or the outer polymer layer 210 may eachindependently include any suitable polymer compositions, such as thosedisclosed in the following publications: U.S. Pat. Nos. 4,170,579 and4,610,769 to Bosso et al., U.S. Pat. No. 5,096,556 to Corrigan et al.,U.S. Pat. No. 4,432,850 to Moriarity et al., and U.S. Pat. No. 4,689,131to Roue, all of which are incorporated by reference herein in theirentirety. In certain instances, the top polymer layer 210 includes anacrylate, with or without a pigment.

The article 200 may be coated according to a method generally shown at300 as depicted in FIG. 3. In one embodiment, the method 300 includes astep 312 of forming an oxide layer on a surface having a metal oxidelayer. The method 300 may further include one or more of steps 302, 303,304, 306, 308, 310 and 314.

At step 302, the surface is etched for cleaning and to remove surfaceoxides, using, in particular, an acid etching process.

At step 303, the surface is modified with a conversion coating foranti-corrosion treatment.

At step 304, the conversion coated surface is coated with a first primerlayer mainly to level the surface. This first primer layer may beapplied using any suitable spraying or powder layer process and issubsequently cured. If the substrate is heat stable, such as metal-basedsubstrate, the curing may be done in an oven. If the substrate is heatlabile, such as plastics-based substrate, the curing may be carried outusing ultraviolet light curing.

After cure, the article such as a vehicle wheel is transferred to avacuum chamber such as a PVD vacuum chamber. In this chamber, theexisting cured coating layer is treated with a gas plasma, followed bydeposition of a thin metallic layer. Non-limiting examples of the gasapplied in the gas plasma may include argon, oxygen, nitrogen, air, orcombinations thereof. In certain instances, argon plasma is used in thisstep to provide a relatively more subtle plasma treatment. The gasplasma treatment of the primer layer is performed to enhance adhesion tothe applied metallic layer. In certain instances, the metallic layer isagain subjected to a gas plasma within the PVD vacuum chamber.

At step 306, the surface may be further coated with a second primerlayer. The second primer layer may be chemically different from thefirst primer layer. In this scenario, while the first primer layer ismainly to level the surface, the second primer layer is to prime thesurface for subsequent layers, particular for subsequent application ofthe metallic layer.

At step 308, the surface may be subject to a plasma treatment, such as aplasma using argon gas, to activate the surface for subsequent metalliclayer application.

At step 310, the surface is coated with the metallic layer. One or bothof the steps 310 and 312 may be carried out under vacuum, and in certaininstances, via the application of plasma vapor deposition. With the useof PVD, the oxide composition may be injected into the metallic layer ata relatively high energy such that the thickness of the oxide layer maybe controlled to be extremely thin, such as 1 to 5 nanometers. At thisthickness, the oxide layer is believed to be transparent enough so asnot to reduce the metallic appearance of the underlying metallic layerto any significant degree, while providing benefits in improvingadhesion.

At step 314, the surface may be coated with an outer polymer layer (insome instances, a top polymer layer), which functions as a protectivelayer over the metallic layer from the environment.

The metallic layer 206 may include any suitable metal elements. Suitablemetal elements include transition metals, and those from groups 13 and14 of the periodic table. In certain instances, the metallic layer 206includes chrome, aluminum, or alloys thereof.

The oxide layer 208 may include one or more oxides selected from thegroup consisting of oxides of electropositive elements, oxides ofelectronegative elements, oxides of amphoteric elements, andcombinations thereof, as long as at least one of the oxides being anoxide of a metal different from the metal included in the metallic layer206. In certain instances, the oxide layer 208 includes one or more of atitanium oxide (TiO₂), a silicon oxide (SiO₂), nickel oxide (Ni₂O₃), tinoxide (SnO₂), and/or aluminum oxide (Al₂O₃).

Non-limiting examples of the oxide of the oxide layer 208 include anoxide of one or more elements of the first row of transition metals suchas nickel, iron, cobalt, copper, and zinc, or those from the second rowof transition metals such as zirconium or yttrium. Without wanting to belimited to any particular theory, it is believed that these metals arecapable of forming oxides in the form of hydroxides M(OH)_(x). Metalhydroxides M(OH)_(x) possess exchangeable hydrogen atoms that are ableto form strong and durable covalent bonds with coupling agents in theouter polymer layer 210. For instance, −c=n cyano groups in the outerpolymer layer 210 may react to form urethane linkages, and siloxanecoupling agents will form M-O—Si bonds. Thus the metal oxide binder canbe matched with specific coupling agents in the outer polymer layer 210to meet necessary bonding requirements.

In certain instances, the metallic layer 206 includes a first metallicsurface contacting the oxide layer, a second metallic surface, and ametallic bulk spacing apart the first and second metallic surfaces, thefirst metallic surface includes an increased concentration of polargroups relative to the second metallic surface. The polar groups includehydroxyl groups OH⁻. In certain particular instances, the concentrationof the polar groups, and hydroxyl groups in particular, of the firstmetallic surface is at least 5 percent, 10 percent, 15 percent or 20percent greater in atomic weight relative to that of the second metallicsurface.

In certain other instances, the polymer layer 210 includes a firstpolymer surface contacting the oxide layer, a second polymer surface,and a polymer bulk spacing apart the first and second polymer surfaces,the first polymer surface includes an increased concentration of polargroups relative to the second polymer surface. The polar groups includehydroxyl groups OH⁻. In certain particular instances, the concentrationof the polar groups, and hydroxyl groups in particular, of the firstpolymer surface is at least 5 percent, 10 percent, 15 percent or 20percent greater in atomic weight relative to that of the second polymersurface.

In certain instances, the thickness of the oxide layer 208 is relativelysmall to not impart a color change to the underlying metallic layer inany significant degree. In certain instances, the thickness of the oxidelayer 208 is less than 10 nm, and particularly 1 to 5 nanometers.

In one or more embodiment, the parameter of the color change can beexpressed, according to the International Commission on Illumination(CIE), as ΔE*_(ab) in terms of the CIELAB color space by the equation,

ΔE* _(ab)=√{square root over ((ΔL*)²+(Δa*)²+(Δb*)²)}

where is L is the color brightness, and a and b are the complimentarycolor-opponent dimensions. A non-limiting example of the color changedetermination may be found according to Hans G. Völz, “Industrial ColorTesting—Fundamentals and Techniques”, second, completely revisededition, translated by Ben Teague, Wiley-VCH, New York (2001), which isincorporated by reference herein in its entirety.

In certain instances, the oxide layer 208 as deposited onto the metalliclayer 206 is relatively thin such that ΔE*, the color difference of themetallic layer 206 before and after deposition of the oxide layer 208,is less than 2.3, a number associated with a “just noticeabledifference” of color differences to the human eye. In certain particularinstances, ΔE* is less than 1.0, which is identified as a colordifference indistinguishable to the human eye.

The thickness of the oxide layer 208 may be determined using anysuitable methods. A non-limiting example involves the use of ion sputterdepth profiling, coupled with a surface sensitive analysis techniquesuch as Auger electron spectroscopy (AES), X-ray photoelectronspectroscopy (XPS), and secondary ion mass spectrometry (SIMS). In thismethod, a beam of ions, typically rare gas ions such as argon, isdirected at the surface of a solid. These ions interact with the surfacein a process called a collision cascade. Material is removed from thesurface by ion sputtering. Over time this process removes material fromthe surface, exposing subsurface layers. These are measured by one ofthe above mentioned surface analysis techniques. By measuring thesurface composition as a function of sputter time, the composition andthickness of thin films can be determined. A reference for the methodmay be found in Hofmann, S., “Quantitative Depth Profiling is SurfaceAnalysis: A Review”, Surface and Interface Analysis, 2(4) 148 (1980),which is incorporated by reference herein in its entirety.

Another non-limiting example of the method involves ellipsometry. Thesample is illuminated with a beam of polarized light and the resultingchange in polarization of the reflected beam is measured. The degree ofpolarization change that occurs is determined by the optical constantsof the thin film, including the film thickness. A reference for thismethod may be found on pages 35 to 45 of Tomkins, H. G., “A users Guideto Ellipsometry, New York, 1993, Academic Press, Inc., relevant contentof which is incorporated by reference herein in its entirety.

Although being directed to a wheel, the above described layer structureand/or method of forming are equally applicable to any suitablesubstrates and surfaces thereof, including plastics, metals, polymers,and combinations thereof.

Examples

A 200 nm layer of chrome is deposited by plasma vapor deposition (PVD)in an argon atmosphere at a partial pressure of 11 mTorr onto asubstrate using a Perkin-Elmer ULTEK model 2400 RF sputtering system. Apaint layer of a carbamate coat composition at 50 μm thickness isapplied over the chrome layer and baked to cure.

A second chrome layer is deposited in an identical manner onto acompanion sample, onto which is subsequently deposited by PVD a siliconoxide (silica) layer at a thickness of 5 nm. The silica layer is thinenough to be essentially transparent and not obscure the coloration ofthe chrome. A clear carbamate paint layer of 50 μm thickness is thenapplied over the silica layer and baked to cure.

A third chrome layer is deposited in an identical manner onto acompanion sample, onto which is subsequently deposited by PVD a titaniumoxide (titania) layer at a thickness of 5 nm. The titania layer is thinenough to be essentially transparent and not to obscure the colorationof the chrome. A clear carbamate paint layer of 50 μm thickness is thenapplied over the titania layer and baked to cure.

A cross-hatch adhesion test is performed on each sample to test therelative adhesion strength of the carbamate paint layer to theunderlying chrome layer, or chrome layer coated with an oxide binderlayer. The cross-hatch adhesion test may be carried out according toStandard Test Methods for Measuring Adhesion by Tape Test, ASTM D3359.

These tests reveal a 98% delamination of the carbamate paint layer fromthe chrome layer, a 49% delamination of the carbamate paint layer fromthe chrome layer coated with the silica binder layer, and a 6%delamination of the carbamate paint layer from the chrome layer coatedwith the titania binder layer. The experiments reveal that adhesion tochrome can be greatly improved, or delamination failure can be greatlyreduced, by the addition of an oxide binder layer.

For this experiment a carbamate paint system is utilized as it is ableto readily differentiate adhesion strength between the layers tested. Inpractice, other paint systems such as acrylic paints or epoxy paintsmight likely yield stronger adhesion to the chrome layer, but wouldstill be susceptible to adhesion failure in durability when subjected totesting at elevated humidity or when subjected to rapid changes intemperature without the exceptional durability imparted by an oxidelayer.

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

1. (canceled)
 2. A method comprising: overlaying a primer polymer layeronto a substrate surface; overlaying a chrome metallic layer onto theprimer polymer; depositing a plasma vapor deposited (PVD) oxide layer ofa thickness of 1 to 5 nanometers onto the chrome metallic layer andhaving a parameter of color change of the underlying chrome metalliclayer determined according to the following equation:ΔE* _(ab)=√{square root over ((ΔL*)²+(Δa*)²+(Δb*)²)} wherein L is acolor brightness of the chrome metallic layer, and a and b arecolor-component dimensions of the PVD oxide and chrome metallic layers,wherein ΔE*_(ab) is less than 2.3; and overlaying an exposed polymericlayer onto the PVD oxide layer to form a protective layer at theinterface between the exposed polymeric layer and the oxide layer. 3.The method of claim 2, wherein the protective layer directly contactsthe exposed polymeric layer and the oxide layer.
 4. The method of claim2, wherein the protective layer includes urethane linkages formedbetween the exposed polymeric layer and the oxide layer.
 5. The methodof claim 2, wherein the protective layer includes M-O—Si bonds formedbetween the exposed polymeric layer and the oxide layer.
 6. The methodof claim 5, wherein the exposed polymeric layer includes a siloxanecoupling agent.
 7. The method of claim 2, wherein the PVD oxide layerincludes titanium oxide.
 8. The method of claim 2, wherein the exposedpolymeric layer includes a carbamate clearcoat.
 9. A method comprising:overlaying a primer polymer layer onto a substrate surface; overlaying achrome metallic layer onto the primer polymer; depositing a plasma vapordeposited (PVD) oxide layer of a thickness of 1 to 5 nanometers onto thechrome metallic layer and having a parameter of color change of theunderlying chrome metallic layer determined according to the followingequation:ΔE* _(ab)=√{square root over ((ΔL*)²+(Δa*)²+(Δb*)²)} wherein L is acolor brightness of the chrome metallic layer, and a and b arecolor-component dimensions of the PVD oxide and chrome metallic layers,wherein ΔE*_(ab) is less than 2.3; and overlaying an exposed polymericlayer onto the PVD oxide layer to react the exposed polymeric layer andthe oxide layer to form a protective layer at the interface.
 10. Themethod of claim 9, wherein the protective layer directly contacts theexposed polymeric layer and the oxide layer.
 11. The method of claim 9,wherein the protective layer includes urethane linkages formed betweenthe exposed polymeric layer and the oxide layer.
 12. The method of claim9, wherein the protective layer includes M-O—Si bonds formed between theexposed polymeric layer and the oxide layer.
 13. The method of claim 12,wherein the exposed polymeric layer includes a siloxane coupling agent.14. The method of claim 9, wherein the PVD oxide layer includes titaniumoxide.
 15. The method of claim 9, wherein the exposed polymeric layerincludes a carbamate clearcoat.
 16. A method comprising: depositing aplasma vapor deposited oxide layer of a thickness of 1 to 5 nanometersonto a chrome metallic layer and having a parameter of color change ofthe underlying metallic layer as follows:ΔE* _(ab)=√{square root over ((ΔL*)²+(Δa*)²+(Δb*)²)} wherein L is ametallic layer color brightness, a and b are color-component dimensionsof the oxide and chrome metallic layers, and ΔE*_(ab) is less than 2.3;and overlaying an exposed polymeric layer to form a protective layer.17. The method of claim 16, further comprising overlying an exposedpolymeric layer onto the oxide layer to react the exposed polymericlayer and the oxide layer to form a protective layer at the interface.18. The method of claim 17, wherein the protective layer directlycontacts the exposed polymeric layer and the oxide layer.
 19. The methodof claim 17, wherein the protective layer includes urethane linkagesformed between the exposed polymeric layer and the oxide layer.
 20. Themethod of claim 17, wherein the protective layer includes M—O—Si bondsformed between the exposed polymeric layer and the oxide layer.
 21. Themethod of claim 20, wherein the exposed polymeric layer includes asiloxane coupling agent.